Signature retrieval and matching for media monitoring

ABSTRACT

An example apparatus includes means for querying a first table to perform a first query of the first table using a hash corresponding to a first site signature, the first table including hash keys corresponding to respective reference signatures, the first query to obtain, from the first table, first qualifier data descriptive of a first reference signature corresponding to a first hash key; means for querying a second table to perform a second query of the second table, the second query to obtain a plurality of blocks of reference signatures; means for comparing a first block of site signatures with the plurality of blocks of reference signatures, the first block of site signatures to include the first site signature; and means for crediting media as corresponding to reference media represented by the first reference signature when the first block of site signatures matches the plurality of blocks of reference signatures.

RELATED APPLICATION(S)

This patent arises from a continuation of U.S. patent application Ser.No. 15/607,006, filed on May 26, 2017, now U.S. Pat. No. ______, whichis a continuation of U.S. patent application Ser. No. 14/469,245, filedAug. 26, 2014, now U.S. Pat. No. 9,668,020, which claims the benefit ofand priority from U.S. Provisional Application Ser. No. 61/976,168,entitled “SIGNATURE RETRIEVAL AND MATCHING FOR MEDIA MONITORING” filedon Apr. 7, 2014. U.S. patent application Ser. No. 15/607,006, U.S.patent application Ser. No. 14/469,245, and U.S. Provisional ApplicationSer. No. 61/976,168 are hereby incorporated by reference in theirentireties. Priority to U.S. Provisional Application Ser. No.61/976,168, U.S. patent application Ser. No. 14/469,245, and U.S. patentapplication Ser. No. 15/607,006 is hereby claimed.

FIELD OF THE DISCLOSURE

This disclosure relates generally to media monitoring and, moreparticularly, to signature retrieval and matching for media monitoring.

BACKGROUND

A media monitoring system typically includes one or more device metersto monitor the media presented by one or more media devices located atone or more monitored sites. Such a device meter can use watermarksdecoded from the presented media and/or signatures (also referred to asmedia fingerprints or just fingerprints) generated from the presentedmedia, or both, to monitor (e.g., identify and/or track) the media beingpresented by a media device. For example, identification codes, such aswatermarks, ancillary codes, etc., may be transmitted within mediasignals. Identification codes are data that are transmitted with media(e.g., inserted into the audio, video, or metadata stream of media) touniquely identify broadcasters and/or the media (e.g., content oradvertisements), and/or are associated with the media for anotherpurpose, such as tuning (e.g., packet identifier headers (“PIDs”) usedfor digital broadcasting). Codes are typically extracted using adecoding operation.

In contrast, signatures are a representation of some characteristic ofthe media signal (e.g., a characteristic of the frequency spectrum ofthe signal). Signatures can be thought of as fingerprints. They aretypically not dependent upon insertion of identification codes in themedia but, instead, preferably reflect an inherent characteristic of themedia and/or the signal transporting the media. Systems to utilize codesand/or signatures for audience measurement are long known. See, forexample, Thomas, U.S. Pat. No. 5,481,294, which is hereby incorporatedby reference in its entirety.

When signatures are used for media monitoring, signatures of themonitored media (referred to herein as site signatures) are generated bythe device meter and compared to reference signatures representative ofreference media known to the media monitoring system. When a match isfound, the media corresponding to the site signature being processed canbe identified as corresponding to the reference media represented by thematching reference signature(s). In many media monitoring systems, thedevice meters provide their generated site signatures to a dataprocessing facility or other centralized processing site for comparisonwith the reference signatures that are representative of the referencemedia available for presentation at the respective monitored sites. Suchcomparison may involve comparing large numbers of site signatures withlarge numbers of reference signatures, especially when the number ofmonitored sites is large and/or the amount of possible reference mediaavailable for consumption is large.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block diagram of an example system capable of performingsignature retrieval and matching for media monitoring as disclosedherein.

FIG. 2 is a block diagram of an example monitored site that may beincluded in the example system of FIG. 1.

FIG. 3 is a block diagram of an example media monitoring system that maybe included in the example system of FIG. 1.

FIG. 4 illustrates example site signatures that may be obtained from theexample monitored site of FIG. 2.

FIG. 5 illustrates example reference signatures that may be obtainedfrom the example media monitoring system of FIG. 3.

FIG. 6 is a block diagram of an example crediting facility that may beincluded in the example system of FIG. 1.

FIG. 7 illustrates an example hash table and an example block table thatmay be used by the example crediting facility of FIG. 6 to performsignature retrieval and matching for media monitoring as disclosedherein.

FIG. 8 illustrates an example signature matching operation capable ofbeing performed by the example crediting facility of FIG. 6.

FIG. 9 is a flowchart representative of first example machine readableinstructions that may be executed to implement signature retrieval andmatching for media monitoring in the example crediting facility of FIG.6.

FIG. 10 is a flowchart representative of second example machine readableinstructions that may be executed to implement signature retrieval andmatching for media monitoring in the example crediting facility of FIG.6.

FIG. 11 is a flowchart representative of example machine readableinstructions that may be executed to implement candidateprequalification in the example crediting facility of FIG. 6.

FIG. 12 is a block diagram of an example processor platform that mayexecute the example machine readable instructions of FIGS. 9, 10 and/or11 to implement the example system of FIG. 1 and/or the examplecrediting facility of FIG. 6.

Wherever possible, the same reference numbers will be used throughoutthe drawing(s) and accompanying written description to refer to the sameor like parts, elements, etc.

DETAILED DESCRIPTION

Methods, apparatus, systems and articles of manufacture (e.g., physicalstorage media, structures, etc.) to perform signature retrieval andmatching for media monitoring are disclosed herein. Some examplesignature retrieval and matching methods disclosed herein includequerying a first table using a first site signature obtained from amonitored site. For example, the first table can include hash keyscorresponding to respective reference signatures, and can furtherinclude respective qualifier data descriptive of respective ones of thereference signatures (and/or descriptive of reference media representedby the respective ones of the reference signatures). Such examplemethods can also include querying a second table using first qualifierdata obtained from querying the first table using the first sitesignature. For example, the first qualifier data can be descriptive of afirst reference signature (and/or first reference media represented bythe first reference signature) corresponding to a first hash keydetermined to match the first site signature. Such example methods canfurther include comparing a first block of site signatures with aportion of a plurality of blocks of reference signatures obtained fromquerying the second table using the first qualifier data.

In some such examples, the first qualifier data includes a firsttimestamp associated with a first block of reference signaturesincluding the first reference signature. In some such examples, thefirst qualifier data also includes first media identification dataidentifying first reference media represented by the first referencesignature.

In some such examples, the plurality of blocks of reference signaturesobtained from querying the second table using the first qualifier datainclude: (1) the first block of reference signatures representative ofthe first reference media and associated with the first timestamp, (2) asecond block of reference signatures representative of the firstreference media and associated with a second timestamp preceding thefirst timestamp, and (3) a third block of reference signaturesrepresentative of the first reference media and associated with a thirdtimestamp following the first timestamp. In some such examples, thefirst qualifier data further includes a first offset specifying aposition of the first reference signature in the first block ofreference signatures, and the first block of site signatures includesneighboring site signatures of the first site signature. Some suchexample methods further include aligning the first block of sitesignatures with a portion of the first, second and third blocks ofreference signatures based on the offset. Such example methods can alsoinclude comparing the first block of site signatures with the portion ofthe first, second and third blocks of reference signatures.

Additionally or alternatively, in some such examples, the firstreference signature is representative of first reference media, and theplurality of blocks of reference signatures is a first plurality ofblocks of reference signatures representative of the first referencemedia. Some such example methods further include querying the secondtable using second qualifier data obtained from querying the first tableusing the first site signature. For example, the second qualifier datacan be descriptive of a second reference signature corresponding to asecond hash key determined to match the first site signature, and thesecond reference signature can be representative of second referencemedia. Such example methods can also include comparing the first blockof site signatures with a portion of a second plurality of blocks ofreference signatures obtained from querying the second table using thesecond qualifier data. For example, the second plurality of blocks ofreference signatures can be representative of the second referencemedia.

Additionally or alternatively, some such example methods can alsoinclude obtaining the first hash key, the first qualifier data and firstvalue data associated with the first hash key in response to queryingthe first table using a first site signature. Some such example methodscan also include using the first value data to prequalify the first hashkey as a candidate for subsequent signature processing associated withthe first site signature. For example, some such example methods canfurther include obtaining a second hash key, second qualifier data andsecond value data associated with the second hash key in response toquerying the first table using a first site signature. In such examples,the second hash key can have been determined to match the first sitesignature, and the second qualifier data can be descriptive of a secondreference signature corresponding to the second hash key. Such examplemethods can also include querying the second table using the secondqualifier data in response to a successful prequalification of thesecond hash key based on the second value data, but not querying thesecond table using the second qualifier data in response to anunsuccessful prequalification of the second hash key based on the secondvalue data.

Furthermore, in some such examples, the first reference signature isrepresentative of first reference media, the first value data includes asecond hash key and a third hash key both representative of the firstreference media, and the second hash key precedes the first hash key intime, whereas the third hash key follows the first hash key in time. Insome such examples, using the first value data to prequalify the firsthash key includes determining prequalification of the first hash key issuccessful in response to determining that the second hash key matches asecond site signature preceding the first site signature in time andthat the third hash key matches a third site signature following thefirst site signature in time. In some such examples, using the firstvalue data to prequalify the first hash key also includes determiningprequalification of the first hash key is unsuccessful in response todetermining that at least one of the second hash key fails to match thesecond site signature or the third hash key fails to match the thirdsite signature.

These and other example methods, apparatus, systems and articles ofmanufacture (e.g., physical storage media, structures, etc.) to performsignature retrieval and matching for media monitoring are disclosed ingreater detail below.

As mentioned above, in media monitoring systems employing mediasignatures, the device meters monitoring media presented by mediadevices at monitored sites typically provide their generated sitesignatures to a data processing facility or other centralized processingsite for comparison with the reference signatures that arerepresentative of the possible reference media available forpresentation at the respective monitored sites. In prior mediamonitoring systems, the central data processing facility may store thereference signatures in random access memory (RAM) for comparison withthe site signatures obtained from the monitored sites. However, as theamount of possible reference media available for presentation increases,the number of possible reference signatures to be compared alsoincreases. In prior media monitoring systems, the increasing number ofreferences signatures requires more and more RAM to store the referencesignatures for comparison, to the point at which the amount of RAM maybecome cost prohibitive and/or unwieldy to manage.

In contrast, media monitoring systems employing signature retrieval andmatching as disclosed herein can perform signature matching moreefficiently than prior systems. Some example media monitoring systemsemploying signature retrieval and matching as disclosed herein utilize adatabase employing a double index hashing strategy in which a firsttable—a hash table—is stored in RAM and queried using site signaturesobtained from monitored sites to retrieve candidate reference signaturesfor further examination. The first hash table can be relativelylightweight and have a smaller RAM footprint than that of prior mediamonitoring systems. The double index hashing strategy of such examplesalso utilizes a second table—a block table—storing blocks of referencesignatures that can be retrieved for matching using the candidatereference signatures retrieved from the hash table. The block table neednot be stored in RAM (although it could be), and may or may not bestored remotely from the hash table. The (relatively few) blocks ofsignatures retrieved from the block table can be temporarily stored inRAM for signature matching. In some examples, signature matchingprocessing is offloaded to servers or other computing devicesimplementing the block table, thereby supporting parallel and/ordistributed data processing.

Turning to the figures, a block diagram of an example system 100 capableof performing signature retrieval and matching for media monitoring asdisclosed herein is illustrated in FIG. 1. The example system 100 ofFIG. 1 includes one or more example media distributor(s) 105 todistribute media for presentation by media devices. A media distributor105 can correspond to any type of media distributor, such as atelevision station, a cable network, a satellite network (e.g.,television or radio), a radio station, a streaming media service (e.g.,such as Hulu™, Netflix®, etc.), etc. As such, the media distributed bythe media distributor(s) 105 can correspond to any type of media, suchas television programming, radio programming, multimedia (e.g., audioand/or visual) data, etc. In the illustrated example, the mediadistributor(s) 105 can distribute a particular piece of media (e.g.,such as a particular television program, a particular radio program, aparticular movie, etc.) to recipients (e.g., television viewers, radiolisteners, computer users, electronic device users, etc.) via one ormore example distribution media 110 (e.g., such a one or more radiofrequency, cable and/or satellite television and/or radio channels, oneor more networks carrying one or more digital transport channels, etc.).

In the example system 100 of FIG. 1, the media distributor(s) 105distribute media via the distribution media 110 to one or more examplemonitored sites 120 that, for example, correspond to one or morepanelists selected (e.g., statistically) for inclusion in an audiencemeasurement panel, media monitoring survey, etc. Each monitored site 120includes one or more media devices to present the media received at themonitored site. Each monitored site 120 also includes one or more devicemeters to monitor the media presented by these media device(s). Forexample, a device meter at a particular monitored site 120 can determinemetering data that may identify and/or be used to identify mediapresented by a media device (and, thus, infer media exposure) at themonitored site 120. In some examples, the monitored site 120 alsoincludes a people meter to determine audience identification data (alsoreferred to as demographic data, people meter data, etc.) identifyingthe audience members (e.g., panelists) being exposed to the monitoredmedia, and/or in the vicinity of the monitored media device, etc. Insuch examples, the device meter combines the metering data with theaudience identification data to determine audience measurement datacharacterizing media exposure at the monitored site 120. The devicemeter can then store and report the metering data (or audiencemeasurement data) to an example crediting facility 115 via an examplereporting medium 125. In the illustrated example, the reporting medium125 can be any type of data transmission medium, such as one or moredata networks (e.g., such as the Internet), one or more mobile telephone(e.g., cellular) networks, a dial-up connection, etc. An exampleimplementation of a monitored site 120 is illustrated in FIG. 2, whichis described in greater detail below.

In the system 100 of the illustrated example, the crediting facility 115performs signature retrieval and matching for media monitoring asdisclosed herein. Unlike media monitoring techniques based on codesand/or watermarks included with and/or embedded in the monitored media,signature-based media monitoring techniques generally use one or moreinherent characteristics of the monitored media during a signaturesampling interval to generate a substantially unique proxy for themedia. Such a proxy is referred to as a signature or media fingerprint,and can take the form of a series of bits, data values, a waveform,etc., representative of the media signal(s) (e.g., an audio signaland/or a video signal) forming the media presentation being monitored. Agood signature is usually one that is repeatable when processing thesame media presentation, but that is unique relative to other(different) presentations of other (different) media. Thus, as usedherein, a signature is a representation of some characteristic of themedia signal (e.g., a characteristic of the frequency spectrum of thesignal) which can be used to identify the signal, and can be thought ofas a fingerprint. Signatures are typically not dependent upon insertionof identification codes in the media, but instead preferably reflect aninherent characteristic of the media and/or the signal transporting themedia. Systems to utilize codes and/or signatures for audiencemeasurement are long known. See, for example, Thomas, U.S. Pat. No.5,481,294, which is hereby incorporated by reference in its entirety.

In the example system 100 of FIG. 1, signature-based media monitoringgenerally involves a device meter determining (e.g., generating) sitesignature(s) (also referred to as collected signature(s) or meteredsignature(s)) representative of a media signal (e.g., an audio signaland/or a video signal) output by a monitored media device at a monitoredsite 120. The device meter at the monitoring site 120 includes the sitesignature(s) in the metering data reported to the example creditingfacility 115. The crediting facility 115 then compares the sitesignature(s) to one or more references signatures corresponding to known(e.g., reference) media. Various comparison criteria, such as across-correlation value, a Hamming distance, population (POP) count,etc., can be evaluated to determine whether a site signature (or blockof site signatures) matches a particular reference signature (or blockof reference signatures). When a match between the site signature(s) andone of (or a block of) the reference signatures is found, the monitoredmedia represented by the site signature(s) can be identified ascorresponding to the particular reference media represented by thereference signature(s) that matched the site signature(s). Becauseattributes, such as an identifier of the media, a presentation time, abroadcast channel, etc., are collected and, thus, known for thereference media represented by the matching reference signature(s), thecrediting facility 115 may associate the monitored media with these sameattributes of the matching reference media. The crediting facility 115can then use the identified attributes of the monitored media to performany appropriate post-processing to, for example, determine audienceratings information, identify targeted advertising to be provided to themonitored site 120, etc.

The crediting facility 115 of the illustrated example employs signatureretrieval and matching as disclosed herein to facilitate efficientretrieval of reference signatures for comparison with the sitesignatures obtained from the monitored sites 120. As disclosed infurther detail below, the example crediting facility 115 utilizes adatabase employing a double index hashing strategy involving a firsttable, referred to herein as a hash table, and a second table, referredto herein as a block table. The hash table is arranged such that eachentry corresponds to a reference signature and is indexed using a hashkey, which may correspond to a hash of the reference signature or thedata value of the reference signature itself. The hash table entry for aparticular reference signature also includes qualifier data descriptiveof the reference signature and, in at least some examples, value datathat may be used to prequalify the reference signature as a goodcandidate for further signature matching processing, as described infurther detail below. The block table is arranged such that each entrycorresponds to a particular value, or combination of values, of thequalifier data and, thus, is indexed using qualifier data retrieved inresponse to querying the hash table. The block table entry for aparticular value, or combination of values, of the qualifier data alsoincludes blocks of reference signatures corresponding to that qualifierdata, which can be retrieved for comparison with a block of sitesignature(s) reported by the device meter at a monitored site 120.Operation of the crediting facility 115 to use the hash table and blocktable for signature retrieval and matching is described in furtherdetail below in connection with the example implementation of thecrediting facility 115 illustrated in FIG. 6.

The example system 100 of FIG. 1 also includes an example mediamonitoring system (MMS) 130 to generate some or all of the referencesignatures used by the crediting facility 115. As described in furtherdetail below, in some examples, the MMS 130 is located separately fromthe monitored site(s) 120 and monitors media distributions by some orall of the media distributor(s) 105. The MMS 130 determines referencesignatures from the media distributions, which correspond to thepossible media that could be received by the monitored site(s) 120. Forexample, for each media distribution monitored by the MMS 130, the MMS130 generates respective reference signatures (e.g., blocks of referencesignatures associated with a signature monitoring interval), timestampsthe reference signatures with time information (e.g., such as day and/ortime-of-day information) corresponding to when the monitored media wasreceived at the MMS 130, and associates media identification informationwith the reference signatures. The MMS 130 then stores and reports thetimestamped reference signatures and media identification information tothe crediting facility 115 via an example reporting medium 135. In theillustrated example, the reporting medium 135 can be any type of datatransmission medium, such as one or more data networks (e.g., such asthe Internet), one or more mobile telephone (e.g., cellular) networks, adial-up connection, etc. An example implementation of the MMS 130 isillustrated in FIG. 3, which is described in greater detail below.

A block diagram of an example implementation of one of the monitoredsites 120 of FIG. 1 is illustrated in FIG. 2. The example monitored site120 of FIG. 2 includes an example media presentation device 205 (alsoreferred to herein as a media device 205) to present media received viathe distribution medium 110. The media presentation device 205 cancorrespond to any type of media device, such as a set-top box, atelevision, a radio, a multimedia computer system, tablet computer, aportable digital assistant, a cellular/mobile smartphone, etc.

The example monitored site 120 of FIG. 2 also includes an example devicemeter 210, also referred to as a meter 210, a site meter 210, a siteunit 210, a home unit 210, a media meter 210, etc., to monitor mediapresented by the media device 205. In the illustrated example, the mediamonitored by the device meter 210 can correspond to any type of mediapresentable by the media device 205. For example, monitored media can bemedia content, such a television programs, radio programs, movies, etc.,and/or commercials, advertisements, etc. In the illustrated example, thedevice meter 210 determines metering data that may identify and/or beused to identify media exposure (and, thus, infer media consumption) atthe monitored site 120. The metering data determined by the exampledevice meter 210 includes site signatures representative of the mediapresented by the media device 205.

For example, in the example monitored site 120 of FIG. 2, the devicemeter 210 may utilize invasive monitoring involving one or more physicalconnections to the media device 205, and/or non-invasive monitoring notinvolving any physical connection to the media device 205, to obtainaccess to one or more media signals corresponding to the media beingpresented by the media device 205. In some examples, the device meter210 may process audio signals obtained from the media device 205 via amicrophone and/or other audio sensor(s), and/or via a direct cableconnection, to generate audio site signatures representative of themedia being presented by the media device 205. Additionally oralternatively, the device meter 210 may process video signals obtainedfrom the media device 205 via a camera and/or other video sensor(s),and/or a direct cable connection, to generate video site signatures(e.g., image signatures) representative of the media being presented bythe media device 205. The site signatures generated by the device meter210 at respective generation intervals can then be compared (e.g., atthe crediting facility 115) with known reference signatures toidentify/monitor the media being presented by the media device 205.

In some examples, the monitored site 120 also includes an example peoplemeter 215 to capture audience identification information describing anaudience being exposed to the media presented by the media device 205.In some examples, the people meter 215 can prompt audience member(s) inthe vicinity of the media device 205 to identify which one or more of apossible group of audience members are present in the audience.Additionally or alternatively, in some examples, the people meter 215can automatically identify one or more individual included in anaudience in the vicinity of the media device 205. In such examples, thedevice meter 210 may combine the metering data identifying (e.g.,directly or indirectly) the media being presented by the media device205 with the audience identification data determined by the people meter215 to form audience measurement data characterizing media exposure(e.g., with demographic information) at the monitored site 120.

The device meter 210 of the illustrated example stores the metering data(or audience measurement data), including the generated site signatures,for reporting to the crediting facility 115 via the reporting medium125. The generated site signatures in the metering data are alsotimestamped to allow the site signatures to be associated with theparticular time when the site signatures were generated. The timestampsalso indicate the time at which the monitored media represented by thesite signatures was presented at the monitored site 120. The devicemeter 210 can report the metering data/audience measurement data(including the site signatures and timestamps) as it is collected (e.g.,streamed), at specified/predetermined time intervals, when a certainamount of data has been collected, when an available memory space isfilled or reaches a threshold capacity (e.g., 90% or some otherpercentage being full), and/or via any other periodic, aperiodic and/orevent-driven schedule.

Example site signatures that can be generated and reported by theexample device meter 210 of FIG. 2 are illustrated in FIG. 4. In theillustrated example of FIG. 4, the device meter 210 generates examplesite signatures 405A-C at successive signature generation intervals. Theexample site signatures 405A-C, collectively referred to as the sitesignatures 405, are digital values represented by some number of bits.For example, each site signature 405A-C may be a digital valuerepresented by 3 bytes, which corresponds to 24 bits. Of course, thesite signatures 405A-C may be digital values represented by a differentnumber of bits. As described above, the digital values making up thesite signatures 405A-C may correspond to, for example, spectral-domainvalues, time-domain values and/or values of other characteristics of themedia signal(s) presented by the media device 205 monitored by thedevice meter 210.

In the illustrated example of FIG. 4, the device meter 210 associatesthe site signatures 405A-C with respective example timestamps 410A-C,collectively referred to as the timestamps 410, as well as othermetering metadata, such as a meter identifier, one or more panelistidentifiers, etc. The example timestamp 410A can be a day/time valueindicating the time at which the respective site signature 405A wasgenerated. For example, the device meter 210 may be configured togenerate site signatures at a particular signature generation interval(e.g., approximately a 15 millisecond (ms) interval, corresponding togenerating 64 signatures per second, or at some other interval). In suchexamples, the timestamps 410A-C can have sufficient resolution toidentify the particular signature generation interval at which aparticular one of the site signatures 405A-C was generated. Althougheach site signature 405A-C is associated with a respective timestamp410A-C in the example of FIG. 4, in other examples, multiple sitesignatures (e.g., a block of site signatures) may be associated with asingle timestamp (e.g., which identifies the starting time at which theblock of site signatures was generated).

A block diagram of an example implementation of the MMS 130 of FIG. 1 isillustrated in FIG. 3. As discussed above, the MMS 130 may be locatedseparately from the monitored site(s) 120 and monitors one, some or allof the different media being distributed by the media distributor(s) 105via the distribution media 110. In the illustrated example of FIG. 3,the MMS 130 includes one or more media receivers 305 to receive mediabeing distributed by the media distributor(s) 105 via the distributionmedia 110. For example, the media receiver(s) 305 can include multiplereceivers assigned to respective media distributors 105, such asparticular television channels/networks, particular radiochannels/networks, particular streaming services, etc. Additionally oralternatively, one or more of the media receiver(s) 305 can be shared(e.g., time-multiplexed) among multiple media distributors 105.

The example MMS 130 of FIG. 3 also includes one or more signaturegenerators 310 to generate reference signatures representative of themedia received by the media receiver(s) 305. For example, the signaturegenerator(s) 310 can include audio signature generator(s) to generateaudio signatures representative of the audio signal(s) corresponding toaudio portion(s) of the media received by the media receiver(s) 305.Additionally or alternatively, the signature generator(s) 310 caninclude video signature generator(s) to generate video (e.g., image)signatures representative of the video signal(s) corresponding to videoportion(s) of the media received by the media receiver(s) 305. As such,in some examples, the signature generator(s) 310 may implement signaturegeneration technique(s) similar to those implemented by the devicemeter(s) 210 at the monitored sites(s) 120.

The signatures generated by the signature generator(s) 310 are referencesignatures that can be used (e.g., by the crediting facility 115) toidentify corresponding media being distributed by the mediadistributor(s) 105. For example, for each media distribution receivedand processed by the MMS 130, the reference signatures output from thesignature generator(s) are associated with media identification data(e.g., such as a source identifier, a stream identifier, etc., asdescribed in further detail) identifying the particular mediarepresented by the reference signatures. Such media identification datacan be known to the MMS 130 based on, for example, the known associationof the media receiver(s) 305 to the respective media distributor(s) 105.

The example MMS 130 of FIG. 3 further includes one or more timedeterminer(s) 315 to determine time information for association with thereference signatures determined by the signature generator(s) 310. Forexample, a signature generator 310 can trigger a time determiner 315 todetermine time information (e.g., timestamps) indicating when referencesignatures for a particular piece of media were generated and, thus,when the corresponding reference media was received by the respectivemedia receiver 305. The time information can include, for example, theparticular day and/or time-of-day at which a particular block ofreference signatures was generated, which corresponds to the particularday and/or time-of-day at which the media represented by this block ofreference signatures was received by the MMS 130. In some examples, eachsignature generator 310 is associated with a respective time determiner315. In some examples, groups of signature generators 310 are associatedwith a respective time determiner 315. The time determiner(s) 315 caninclude any timing source, such as a clock, timer, etc., capable ofproviding time information having an acceptable accuracy.

Example reference signatures that can be generated and reported by theexample MMS 130 of FIG. 3 are illustrated in FIG. 5. In the illustratedexample of FIG. 5, the MMS 130 generates example reference signatureblocks 505, which contain one or more example reference signatures, atsuccessive signature generation intervals. Each of the referencesignatures included in an example reference signature block 505 is adigital value represented by some number of bits. For example, eachreference signature in the reference signature block 505 may be adigital value represented by 3 bytes, which corresponds to 24 bits. Ofcourse, the reference signatures in the reference signature block 505may be digital values represented by a different number of bits. Asdescribed above, the digital values making up the reference signaturesin the reference signature block 505 may correspond to, for example,spectral-domain values, time-domain values and/or one or more values ofone or more other characteristics of the media signal(s) received by themedia receiver(s) 305 at the MMS 130.

In the illustrated example of FIG. 5, the MMS 130 associates thereference signature block 505 with other reference metadata, such as arespective example timestamp 510 and a respective example mediaidentifier 515. The example timestamp 510 can be a day/time valueindicating the start time at which the reference signature block 505 wasgenerated. For example, a signature generator 310 at the MMS 130 may beconfigured to generate reference signatures at a particular signaturegeneration interval (e.g., approximately a 15 ms interval, correspondingto generating 64 signatures per second, or some other interval). In suchexamples, the timestamp 510 can have sufficient resolution to identifythe start time at which the reference signatures included in thereference signature block 505 were generated. For example, in the caseof the signature generator 310 being configured to generate 64 referencesignatures per second (e.g., corresponding to a signature generationinterval of approximately 15 ms), then the timestamp 510 may have aresolution of 1 second (sec.) if the reference signature block 505contains 64 reference signatures, 2 sec. if the reference signatureblock 505 contains 128 reference signatures, etc. In the illustratedexample of FIG. 5, the media identifier 515 may include a sourceidentifier, a stream identifier, etc., identifying the particularreference media represented by the reference signatures in the referencesignature block 505.

Returning to FIG. 3, the illustrated example MMS 130 also includes anexample data reporter 320 to report reference data to the creditingfacility 115 via the example reporting medium 135. For example, thereference data reported by the example data reporter 320 can includereference signature blocks 505 and associated timestamps 510 and mediaidentifiers 515 generated by the signature generator(s) 310 and the timedeterminer(s) 315. The data reporter 320 can report the reference data(including the reference signature blocks 505, the associated timestamps510 and the media identifiers 515) as it is collected (e.g., streamed),at specified/predetermined time intervals, when a certain amount of datahas been collected, when an available memory space is filled or reachesa threshold capacity (e.g., 90% or some other percentage being full),etc.

A block diagram of an example implementation of the crediting facility115 of FIG. 1 is illustrated in FIG. 6. The block diagram of FIG. 6illustrates structures associated with implementing signature retrievaland matching at the crediting facility 115. Other structures implementedby the crediting facility 115 have been omitted for clarity.

Turning to FIG. 6, the illustrated example crediting facility 115includes an example MMS interface 605 to interface with an MMS, such asthe example MMS 130 of FIGS. 1 and/or 3. As such, the MMS interface 605can be implemented using any interface technology, communicationdevice(s), etc., capable of interfacing with and receiving data via theexample reporting medium 135. The example MMS interface 605 receivesreference data from the MMS 130 including, for example, the referencesignature blocks 505, the associated timestamps 510 and the mediaidentifiers 515.

As mentioned above, the crediting facility 115 of the illustratedexample employs a double index hashing strategy for signature retrievaland matching, which involves a first table, referred to herein as a hashtable, and a second table, referred to herein as a block table.Accordingly, the example crediting facility 115 of FIG. 6 includes anexample hash table populator 610 to populate a hash table to be used bythe crediting facility 115. The example crediting facility 115 of FIG. 6also includes an example block table populator 615 to populate a blocktable to be used by the crediting facility 115. An example hash table710 and an example block table 715 that can be used by the creditingfacility 115 for signature retrieval and matching are illustrated inFIG. 7.

Turning to FIG. 7, the example hash table 710 illustrated thereinincludes entries (e.g., rows) corresponding to the respective referencesignatures received from the MMS 130 via the MMS interface 605. Forexample, each entry of the hash table 710 corresponds to a respectivereference signature and is indexed using an example hash key 712. Thehash key 712 may correspond to a value of the particular referencesignature corresponding to the hash table entry, or may correspond to ahash of the reference signature value (e.g., to reduce data space). Forconvenience, in the following description, the hash key 712 is assumedto correspond to the value of the particular reference signaturecorresponding to the hash table entry.

In the illustrated example, the entry of the hash table 710corresponding to a particular reference signature represented by thehash key 712 also includes example qualifier data 720 descriptive of thereference signature. For example, the qualifier data 720 can includemetadata, such as an example timestamp 722, an example source identifier724, an example stream identifier 726 and an example offset 728. In theillustrated example of FIG. 7, the timestamp 722 included in thequalifier data 720 corresponds to the timestamp 510 of the particularreference signature block 505 reported by the MMS 130 and containing theparticular reference signature corresponding to the hash table entry. Inthe illustrated example of FIG. 7, the source identifier 724 and thestream identifier 726 are obtained from the media identifier 515reported by the MMS 130 for the particular reference signature block 505containing the particular reference signature corresponding to the hashtable entry. In the illustrated example of FIG. 7, the offset 728identifies the position of the particular reference signature, whichcorresponds to the hash table entry, in its respective referencesignature block 505 reported by the MMS 130. As such, in the illustratedexample of FIG. 7, the timestamp 722, source identifier 724, and streamidentifier 726 will be the same for the hash table entries correspondingto reference signatures included in the same reference signature block505. However, the offset 728 will be different for each of these hashtable entries and will provide the particular position of each referencesignature in the reference signature block 505.

In some examples, the entry of the hash table 710 corresponding to aparticular reference signature represented by the hash key 712 furtherincludes example value data 730 that may be used to prequalify thereference signature corresponding to the hash table entry as a goodcandidate for further signature matching processing. In the illustratedexample of FIG. 7, the value data 730 includes an example previous hashkey 732 and an example next hash key 734. The previous hash key 732corresponds to a reference signature preceding the particular referencesignature corresponding to the hash key 712 and having the same sourceidentifier 724 and stream identifier 726. Referring to the particularreference signature corresponding to the hash key 712 as the currentreference signature, then the previous hash key 732 may correspond to areference signature preceding the current signature in the samereference signature block 505, or in the preceding reference signatureblock 505 for the same source identifier 724 and stream identifier 726.In some examples, the previous hash key 732 corresponds to the referencesignature immediately preceding the current reference signature, whereasin other examples, there may be one or more intervening referencesignatures between the current reference signature and the precedingreference signature corresponding to the previous hash key 732. The nexthash key 734 corresponds to a reference signature following theparticular reference signature corresponding to the hash key 712 andhaving the same source identifier 724 and stream identifier 726. Againreferring to the particular reference signature corresponding to thehash key 712 as the current reference signature, then the next hash keymay correspond to a reference signature following the current signaturein the same reference signature block 505, or in the following referencesignature block 505 for the same source identifier 724 and streamidentifier 726. In some examples, the next hash key 734 corresponds tothe reference signature immediately following the current referencesignature, whereas in other examples, there may be one or moreintervening reference signatures between the current reference signatureand the subsequent reference signature corresponding to the previoushash key 732. Similar to the hash key 712, the previous hash key 732 andnext hash key 734 may be equal to the values of their respectivereference signatures, or may correspond to a hash of the respectivereference signature values (e.g., to reduce data space). Forconvenience, in the following description, the previous hash key 732 andnext hash key 734 are assumed to correspond to the values of therespective previous and next reference signatures. Use of the previoushash key 732 and next hash key 734 to prequalify the reference signaturecorresponding to the current hash key 712 is described in further detailbelow.

The example block table 715 illustrated in FIG. 7 includes entriescorresponding to each reference signature block 505 reported by the MMS130. In the example of FIG. 5, each reference block 505 is identifiableusing its respective timestamp 510 and media identifier 515.Accordingly, each entry of the block table 715 is indexed using anexample key 750 including metadata, such as an example timestamp 752, anexample source identifier 754 and an example stream identifier 756. Inthe illustrated example of FIG. 7, the timestamp 752, the sourceidentifier 754 and the stream identifier 756 correspond respectively tothe timestamp 722, the source identifier 724 and the stream identifier726 included in the example qualifier data 720 of the example hash table710. As such, the qualifier data 720 returned in response to queryingthe hash table 710 can be used to index into the example block table715. In the illustrated example of FIG. 7, the timestamp 752 included inthe key 750 corresponds to the timestamp 510 of the particular referencesignature block 505 corresponding to the block table entry. In theillustrated example of FIG. 7, the source identifier 754 and the streamidentifier 756 of the key 750 are obtained from the media identifier 515reported by the MMS 130 for the particular reference signature block 505corresponding to the block table entry.

The entry of the block table 715 corresponding to a particular referencesignature block represented by the key 750 also includes example valuedata 760, which includes the current reference signature block 762corresponding to this entry of the block table 715, as well as theprevious reference signature block 764 and the next reference signatureblock 766. In the illustrated example of FIG. 7, the previous referencesignature block 764 corresponds to the reference signature block 505preceding the current reference signature block 762 in time and that isassociated with the same source identifier 754 and stream identifier 756as the current reference signature block 762. As such, the timestamp 510of the previous reference signature block 764 may be the immediatelypreceding timestamp relative to the timestamp 752. In the illustratedexample of FIG. 7, the next reference signature block 766 corresponds tothe reference signature block 505 following the current referencesignature block 762 in time and that is associated with the same sourceidentifier 754 and stream identifier 756 as the current referencesignature block 762. As such, the timestamp 510 of the next referencesignature block 766 may be the immediately following timestamp relativeto the timestamp 752.

In some examples, the entry of the block table 715 corresponding to aparticular reference signature block represented by the key 750 furtherincludes example qualifier data 770. In the illustrated example of FIG.7, the qualifier data 770 includes example version data 772, which maybe used to specify particular characteristics of the data stored in theblock table 715. For example, FIG. 7 depicts specific example data sizesfor the different data values in the entries of the hash table 710 andthe block table 715. These data sizes may be associated with aparticular value of the version data 772. In such examples, differentvalues of the version data 772 may be used to specify different datasizes, or combinations of sizes, for the different data values in theentries of the block table 715.

In some examples, the hash table 710 and/or the block table 715 areimplemented by one or more databases. For example, the hash table 710and the block table 715 may be implemented by the crediting facility 115using an Apache HBase™ database solution, a Structured Query Language(SQL) database solution, etc.

Returning to FIG. 6, the example hash table populator 610 of theillustrated example receives the reference signature blocks 505 andassociated timestamps 510 and media identifiers 515 from the MMS 130 viathe MMS interface 605. The hash table populator 610 of the illustratedexample then populates the hash table 710, which is stored in an examplehash table storage 620, using the received reference signature blocks505 and associated timestamps 510 and media identifiers 515. Forexample, for a particular received reference signature block 505, thehash table populator 610 populates each reference signature included inthe block 505 as a respective hash key 712 corresponding to a respectiveentry of the hash table 710. The hash table populator 610 of theillustrated example also populates the timestamp 722 for this hash tableentry with the value of the timestamp 510 associated with the referencesignature block 505, and populates the source identifier 724 and thestream identifier 726 for this hash table entry based on the mediaidentifier 515 associated with the reference signature block 505. Thehash table populator 610 further populates the offset 728 for this hashtable entry with the position, in the reference block 505, of theparticular reference signature corresponding to the hash key 712. Insome examples, the hash table populator 610 populates the previous hashkey 732 and the next hash key 734 of the value data 730 with theappropriate previous and next reference signatures relative to theparticular reference signature corresponding to the hash key 712.

In some examples, the example hash table storage 620 is implemented byRAM to enable relatively fast access and processing of the hash table710. For example, the hash table storage 620 can be implemented by thevolatile memory 1214 and/or the local memory 1213 of the exampleprocessor platform 1200 of FIG. 12. In other examples, the hash tablestorage 620 is implemented by any mass storage device, such as one ormore of the example mass storage devices 1228 of the example processorplatform 1200 of FIG. 12. The example processor platform 1200 of FIG. 12is described in further detail below.

The example block table populator 615 receives the reference signatureblocks 505 and associated timestamps 510 and media identifiers 515 fromthe MMS 130 via the MMS interface 605. The block table populator 615 ofthe illustrated example then populates the block table 715, which isstored in an example block table storage 625, using the receivedreference signature blocks 505 and associated timestamps 510 and mediaidentifiers 515. For example, for a particular received referencesignature block 505, the block table populator 615 populates the key 750of an entry in the block table 715 corresponding to the receivedreference signature block 505 as follows. The block table populator 615populates the timestamp 752 of the key 750 for this block table entrywith the value of the timestamp 510 associated with the referencesignature block 505, and populates the source identifier 754 and thestream identifier 756 of the key 750 for this block table entry based onthe media identifier 515 associated with the reference signature block505. The block table populator 615 further populates the currentreference signature block 762 of the value data 760 for this block tableentry with the reference signatures included in the received referencesignature block 505. Additionally, the block table populator 615populates the previous reference signature block 764 and the nextreference signature block 766 with the appropriate previous and nextreference signature blocks relative to the current reference signatureblock 762. In some examples, the block table populator 615 alsopopulates the qualifier data 770 for this block table entry with theappropriate version data 772.

The example block table storage 625 may be implemented by anyappropriate memory, storage device, etc., such as one or more of thevolatile memory 1214, the local memory 1213, the mass storage device1228 of the example processor platform 1200 of FIG. 12. The exampleprocessor platform 1200 of FIG. 12 is described in further detail below.Also, in some examples, the block table storage 625 may correspond tomultiple storages 625 storing multiple block tables 715 (e.g.,remotely).

The example crediting facility 115 of FIG. 6 also includes an examplesite interface 630 to interface with a monitored site, such as theexample monitored site 120 of FIGS. 1 and/or 2. As such, the siteinterface 630 can be implemented using any interface technology,communication device(s), etc., capable of interfacing with and receivingdata via the example reporting medium 125. The example site interface630 receives metering data from the monitored site 120 including, forexample, the site signatures 405 and the associated timestamps 410.

The example crediting facility 115 of FIG. 6 further includes an examplehash table query processor 635 to query the hash table 710 stored in thehash table storage 620 using the site signatures 405 received via thesite interface 630. For example, the hash table query processor 635 canimplement an appropriate database query (e.g., such as an HBase query)to query the hash table 710 using a first site signature, such as thesite signature 405A. In response to the query, the hash table queryprocessor 635 returns one or more hash table entries correspondingrespectively to one or more hash keys 712 (e.g., reference signatures)determined to match the site signature 405A. For example, for aparticular hash key 712 (e.g., reference signature) determined to matchthe site signature 405A, the hash table query processor 635 of theillustrated example returns the qualifier data 720 (e.g., the timestamp722, the source identifier 724, the stream identifier 726 and the offset728) and the value data 730 (e.g., the previous hash key 732 and thenext hash key 734) stored in the hash table entry corresponding to thematching hash key 712.

Because multiple hash keys 712 (e.g., reference signatures) may match aparticular site signature (e.g., the site signature 405A), the examplecrediting facility 115 of FIG. 6 includes an example candidate qualifier640 to prequalify candidate hash keys 712, which have been determined tomatch a particular site signature, for use in subsequent matchingprocessing. For example, the hash table query processor 635 may returnmultiple hash keys 712 (and their associated hash table entries) inresponse to querying the hash table 710. These hash keys 712 arereferred to herein as candidate hash keys 712 because one or more ofthese keys may not actually correspond to the media represented by thesite signature used to query the hash table 710 (e.g., due to falsematches). In such an example, the candidate qualifier 640 examines thecandidate hash keys 712 to determine which ones should be retained asprequalified hash keys 712 that can form the basis for subsequentqueries of the block table 715.

In the illustrated example, the candidate qualifier 640 performsprequalification of a particular candidate hash key 712 using the valuedata 730 associated with the candidate hash key 712. For example, thecandidate qualifier 640 of the illustrated example can obtain theprevious hash key 732 and the next hash key 734 included in the valuedata 730 for the particular candidate hash key 712. As noted above, theprevious hash key 732 corresponds to the hash key (e.g., referencesignature) preceding the hash key 712 in time, and the next hash key 734corresponds to the hash key (e.g., reference signature) following thehash key 712 in time. In such examples, the candidate qualifier 640compares the previous hash key 732 with the neighboring site signaturepreceding, in time, the site signature used to query the hash table 710,and compares the next hash key 734 with the neighboring site signaturefollowing, in time, the site signature used to query the hash table 710.For example, if the site signature 405B is used to query the hash table710, then the candidate qualifier 640 compares the site signature 405Awith the previous hash key 732 and compares the site signature 405C withthe next hash key 734 for the candidate hash key 712 undergoingprequalification. If both comparisons are successful (e.g., the previoushash key 732 matches the previous site signature and the next hash key734 matches the following site signature), then the candidate qualifier640 indicates that prequalification for the particular candidate hashkey 712 is successful and this key is retained for use in querying theblock table 715 (or, in other words, the qualifier data 720 associatedwith the particular candidate hash key 712 is used to query the blocktable 715 in response to a successful prequalification of the particularcandidate hash key 712 based on its associated value data 730, whichincludes the previous hash key 732 and the next hash key 734). Otherwise(e.g., if either comparison is unsuccessful), then the candidatequalifier 640 indicates that prequalification for the particularcandidate hash key 712 is unsuccessful and this key is not retained foruse in querying the block table 715 (or, in other words, the qualifierdata 720 associated with the particular candidate hash key 712 is notused to query the block table 715 in response to an unsuccessfulprequalification of the particular candidate hash key 712 based on itsassociated value data 730, which includes the previous hash key 732 andthe next hash key 734). In some examples, the candidate qualifier 640performs the preceding prequalification process for each candidate hashkey 712 returned in response to a query of the hash table 710.

The example crediting facility 115 of FIG. 6 includes an example blocktable query processor 645 to query the block table 715 stored in theblock table storage 625 using the prequalified candidate hash keys 712(e.g., reference signatures) identified by the candidate qualifier 640.In the illustrated example, for a particular candidate hash key 712returned by the hash table query processor 635 in response to a hashtable query using a particular site signature (e.g., and prequalified bythe candidate qualifier 640), the block table query processor 645 canimplement an appropriate database query (e.g., such as an HBase query)to query the block table 715 using the qualifier data 720 associatedwith the particular candidate hash key 712. For example, the qualifierdata 720 for the particular candidate hash key 712 includes thetimestamp 722, the source identifier 724 and the stream identifier 726,which can be used to query the block table 715 to find a key 750 havinga matching timestamp 752, source identifier 754 and stream identifier756. In response to this block table query, the block table queryprocessor 645 returns the key 750 having the timestamp 752, the sourceidentifier 754 and the stream identifier 756 that match the timestamp722, the source identifier 724 and the stream identifier 726 in thequalifier data 720 for the particular candidate hash key 712.Additionally, the block table query processor 645 returns the currentreference signature block 762, the previous reference signature block764 and the next reference signature block 766 included in the valuedata 760 for this block table entry.

In the illustrated example of FIG. 6, the block table query processor645 provides the current reference signature block 762, the previousreference signature block 764 and the next reference signature block 766obtained from the query of the block table 715 for a particularcandidate hash key 712 to an example signature matcher 650. Thesignature matcher 650 of the illustrated example compares a block ofneighboring site signatures, which includes (e.g., is centered on,begins with, ends with, etc.) the particular site signature used toobtain the particular candidate hash key 712, with an appropriatelyaligned, overlapping portion of the current reference signature block762, the previous reference signature block 764 and/or the nextreference signature block 766 for the particular candidate hash key 712.The appropriate alignment of the site signature block to the overlappingportion of the current, previous and/or next reference signatureblock(s) 762-766 is determined using the offset 728 included in thequalifier data 720 for the particular candidate hash key 712.

The signature matcher 650 uses any appropriate metric to compare thesite signature block with the overlapping portion of the current,previous and/or next reference signature block(s) 762-766. For example,if the site signatures and reference signatures are all digital valuesrepresented by sequences of bits, the signature matcher 650 can use aPOP count to count the number of bits that are different between thesite signature block and the overlapping portion of the current,previous and/or next reference signature block(s) 762-766. If the numberof different bits satisfies/meets (e.g., is less than, or is less thanor equal to) a threshold, the signature matcher 650 determines that thesite signature block matches the overlapping portion of the current,previous and/or next reference signature block(s) 762-766. Conversely,if the number of different bits fails to satisfy/meet (e.g., is greaterthan, or is greater than or equal to) the threshold, the signaturematcher 650 determines that the site signature block fails to match theoverlapping portion of the current, previous and/or next referencesignature block(s) 762-766.

An example matching operation capable of being performed by the examplesignature matcher 650 of FIG. 6 is illustrated in FIG. 8. In theillustrated example of FIG. 8, a first site signature 805 has been usedto query the hash table 710 to obtain a candidate (e.g., andprequalified) hash key 712. The reference signature corresponding tothis candidate hash key 712 is denoted using the reference numeral 812in the example of FIG. 8. A query of the block table 715 using thequalifier data 720 for this candidate hash key 712 returns the current,previous and next reference signature block(s) 762-766. The particularcurrent, previous and next reference signature block(s) 762-766 for thiscandidate hash key 712 are denoted using the respective referencenumerals 862, 864 and 866 in the example of FIG. 8.

The offset 728 included in the qualifier data 720 for this candidatehash key 712 specifies the location of the reference signature 812(which corresponds to this candidate hash key 712) in the currentreference signature block 862. Accordingly, the signature matcher 650 isable to align the site signature 805 (which was used to query the hashtable 710) with the reference signature 812 (which corresponds to thismatching candidate hash key 712) using the offset as shown in theexample of FIG. 8. Furthermore, the example signature matcher 650 forms,from the neighboring received site signatures preceding and followingthe site signature 805 in time, a site signature block 870 centeredabout the site signature 805 and containing a number of site signaturesequal to the number of reference signatures (e.g., 64 signatures, 128signatures, etc.) included in one of the reference signature blocks 862,864 and 866. The signature matcher 650 uses the offset 728 to align thesite signature block 870 with the appropriate portion of the referencesignature blocks 862, 864 and 866 (e.g., which corresponds to a portionof the current and previous reference signature blocks 862 and 864 inthe illustrated example). The signature matcher 650 then determines aPOP count or some other comparison metric to determine whether the sitesignature block 870 matches the aligned, overlapping portion of thereference signature blocks 862, 864 and 866.

FIG. 8 also depicts example hash keys and example site signatures thatcould be used to prequalify the hash key corresponding to the referencesignature 812. In the illustrated example, the reference signature 882corresponds to the previous hash key 732 and the reference signature 884corresponds to the next hash key 734 included in the value data 730 forthe hash key corresponding to the reference signature 812. In theillustrated example, to prequalify the hash key 712 corresponding to thereference signature 812, the example candidate qualifier 640 comparesthe reference signature 882 (or its corresponding hash key) with theneighboring site signature 892 preceding the site signature 805 in time,and compares the reference signature 884 (or its corresponding hash key)with the neighboring site signature 894 preceding the site signature 805in time, as shown.

While example manners of implementing the example crediting facility 115and, more generally, the example system 100 are illustrated in FIGS.1-8, one or more of the elements, processes and/or devices illustratedin FIGS. 1-8 may be combined, divided, re-arranged, omitted, eliminatedand/or implemented in any other way. Further, the example mediadistributor(s) 105, the example monitored site(s) 120, the example MMS130, the example media device 205, the example device meter 210, theexample people meter 215, the example media receiver(s) 305, the examplesignature generator(s) 310, the example time determiner(s) 315, theexample data reporter 320, the example MMS interface 605, the examplehash table populator 610, the example block table populator 615, theexample hash table storage 620, the example block table storage 625, theexample site interface 630, the example hash table query processor 635,the example candidate qualifier 640, the example block table queryprocessor 645, the example signature matcher 650 and/or, more generally,the example crediting facility 115 and/or the example system 100 ofFIGS. 1-8 may be implemented by hardware, software, firmware and/or anycombination of hardware, software and/or firmware. Thus, for example,any of the example media distributor(s) 105, the example monitoredsite(s) 120, the example MMS 130, the example media device 205, theexample device meter 210, the example people meter 215, the examplemedia receiver(s) 305, the example signature generator(s) 310, theexample time determiner(s) 315, the example data reporter 320, theexample MMS interface 605, the example hash table populator 610, theexample block table populator 615, the example hash table storage 620,the example block table storage 625, the example site interface 630, theexample hash table query processor 635, the example candidate qualifier640, the example block table query processor 645, the example signaturematcher 650 and/or, more generally, the example crediting facility 115and/or the example system 100 could be implemented by one or more analogor digital circuit(s), logic circuits, programmable processor(s),application specific integrated circuit(s) (ASIC(s)), programmable logicdevice(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)).When reading any of the apparatus or system claims of this patent tocover a purely software and/or firmware implementation, at least one ofthe example system 100, the example crediting facility 115, the examplemedia distributor(s) 105, the example monitored site(s) 120, the exampleMMS 130, the example media device 205, the example device meter 210, theexample people meter 215, the example media receiver(s) 305, the examplesignature generator(s) 310, the example time determiner(s) 315, theexample data reporter 320, the example MMS interface 605, the examplehash table populator 610, the example block table populator 615, theexample hash table storage 620, the example block table storage 625, theexample site interface 630, the example hash table query processor 635,the example candidate qualifier 640, the example block table queryprocessor 645 and/or the example signature matcher 650 is/are herebyexpressly defined to include a tangible computer readable storage deviceor storage disk such as a memory, a digital versatile disk (DVD), acompact disk (CD), a Blu-ray disk, etc. storing the software and/orfirmware. Further still, the example system 100 and/or the examplecrediting facility 115 may include one or more elements, processesand/or devices in addition to, or instead of, those illustrated in FIGS.1-8, and/or may include more than one of any or all of the illustratedelements, processes and devices.

Flowcharts representative of example machine readable instructions forimplementing the example system 100, the example crediting facility 115,the example media distributor(s) 105, the example monitored site(s) 120,the example MMS 130, the example media device 205, the example devicemeter 210, the example people meter 215, the example media receiver(s)305, the example signature generator(s) 310, the example timedeterminer(s) 315, the example data reporter 320, the example MMSinterface 605, the example hash table populator 610, the example blocktable populator 615, the example hash table storage 620, the exampleblock table storage 625, the example site interface 630, the examplehash table query processor 635, the example candidate qualifier 640, theexample block table query processor 645 and/or the example signaturematcher 650 are shown in FIGS. 9-11. In these examples, the machinereadable instructions comprise one or more programs for execution by aprocessor, such as the processor 1212 shown in the example processorplatform 1200 discussed below in connection with FIG. 12. The one ormore programs, or portion(s) thereof, may be embodied in software storedon a tangible computer readable storage medium such as a CD-ROM, afloppy disk, a hard drive, a digital versatile disk (DVD), a Blu-rayDisk™, or a memory associated with the processor 1212, but the entireprogram or programs and/or portions thereof could alternatively beexecuted by a device other than the processor 1212 and/or embodied infirmware or dedicated hardware (e.g., implemented by an ASIC, a PLD, anFPLD, discrete logic, etc.). Also, one or more of the machine readableinstructions represented by the flowcharts of FIGS. 9-11 may beimplemented manually. Further, although the example program(s) is(are)described with reference to the flowcharts illustrated in FIGS. 9-11,many other methods of implementing the example system 100, the examplecrediting facility 115, the example media distributor(s) 105, theexample monitored site(s) 120, the example MMS 130, the example mediadevice 205, the example device meter 210, the example people meter 215,the example media receiver(s) 305, the example signature generator(s)310, the example time determiner(s) 315, the example data reporter 320,the example MMS interface 605, the example hash table populator 610, theexample block table populator 615, the example hash table storage 620,the example block table storage 625, the example site interface 630, theexample hash table query processor 635, the example candidate qualifier640, the example block table query processor 645 and/or the examplesignature matcher 650 may alternatively be used. For example, withreference to the flowcharts illustrated in FIGS. 9-11, the order ofexecution of the blocks may be changed, and/or some of the blocksdescribed may be changed, eliminated, combined and/or subdivided intomultiple blocks.

As mentioned above, the example processes of FIGS. 9-11 may beimplemented using coded instructions (e.g., computer and/or machinereadable instructions) stored on a tangible computer readable storagemedium such as a hard disk drive, a flash memory, a read-only memory(ROM), a compact disk (CD), a digital versatile disk (DVD), a cache, arandom-access memory (RAM) and/or any other storage device or storagedisk in which information is stored for any duration (e.g., for extendedtime periods, permanently, for brief instances, for temporarilybuffering, and/or for caching of the information). As used herein, theterm tangible computer readable storage medium is expressly defined toinclude any type of computer readable storage device and/or storage diskand to exclude propagating signals and to exclude transmission media. Asused herein, “tangible computer readable storage medium” and “tangiblemachine readable storage medium” are used interchangeably. Additionallyor alternatively, the example processes of FIGS. 9-11 may be implementedusing coded instructions (e.g., computer and/or machine readableinstructions) stored on a non-transitory computer and/or machinereadable medium such as a hard disk drive, a flash memory, a ROM, a CD,a DVD, a cache, a RAM and/or any other storage device or storage disk inwhich information is stored for any duration (e.g., for extended timeperiods, permanently, for brief instances, for temporarily buffering,and/or for caching of the information). As used herein, the termnon-transitory computer readable medium is expressly defined to includeany type of computer readable storage device and/or storage disk and toexclude propagating signals and to exclude transmission media. As usedherein, when the phrase “at least” is used as the transition term in apreamble of a claim, it is open-ended in the same manner as the term“comprising” is open ended. Also, as used herein, the terms “computerreadable” and “machine readable” are considered equivalent unlessindicated otherwise.

A first example program 900 that may be executed to implement theexample crediting facility 115 of FIGS. 1 and/or 6 is represented by theflowchart shown in FIG. 9. With reference to the preceding figures andassociated written descriptions, the example program 900 of FIG. 9begins execution at block 905 at which the example MMS interface 605 ofthe crediting facility 115 receives reference data from the MMS 130 asdescribed above, which includes the reference signature blocks 505, theassociated timestamps 510 and the media identifiers 515. At block 910,the example hash table populator 610 of the crediting facility 115populates, as described above, the example hash table 710 with thereference data received at block 905. At block 915, the example blocktable populator 615 of the crediting facility 115 populates, asdescribed above, the example block table 715 with the reference datareceived at block 905.

In some examples, at block 920, the crediting facility 115 performs hashtable compaction to purge out-of-date reference data from the hash table710. Similarly, in some examples, at block 925 the crediting facility115 performs block table compaction to purge out-of-date reference datafrom the block table 715. For example, in an HBase implementation, thedata included in entries of the hash table 710 and/or the block table715 can be tagged with time-to-live values specifying a duration (e.g.,such as a number of days, weeks, etc.) during which the data should beretained in the respective hash table 710 and/or block table 715. Uponexpiration of the time-to-live values, the crediting facility 115 purgesthe expired hash table data at block 920, and purges the expired blocktable data at block 925.

A second example program 1000 that may be executed to implement theexample crediting facility 115 of FIGS. 1 and/or 6 is represented by theflowchart shown in FIG. 10. With reference to the preceding figures andassociated written descriptions, the example program 1000 of FIG. 10begins execution at block 1005 at which the example site interface 630of the crediting facility 115 receives metering data, which includes thesite signatures 405 and the associated timestamps 410, from a monitoredsite 120, as described above. At block 1010, the example hash tablequery processor 635 of the crediting facility 115 queries the hash table710, as described above, to retrieve candidate hash keys 712 (e.g.,corresponding to respective reference signatures) matching a particularsite signature. At block 1010, the query of the hash table for aparticular site signature returns the candidate hash keys 712 (e.g.,corresponding to respective reference signatures) matching a particularsite signature, as well as the qualifier data 720 and the value data 730for these candidate hash keys 712. At block 1015, the example candidatequalifier 640 of the crediting facility performs candidateprequalification, as described above, to retain the prequalifiedcandidate hash keys 712 to be used in subsequent signature matchingprocessing (and to exclude the other candidate hash keys). Examplemachine readable instructions that may be used to implement theprocessing at block 1015 are illustrated in FIG. 11 and described infurther detail below.

At block 1020, the crediting facility 1020 configures the example blocktable query processor 645 and the example signature matcher 650 toprocess each prequalified candidate hash key 712 retained at block 1015.For example, at block 1025, the block table query processor 645 queriesthe block table 715, as described above, using the qualifier data 720for a given prequalified candidate hash key 712 (e.g., corresponding toa respective reference signature) to retrieve the current, previous andnext reference signature blocks 762-766 corresponding to the givenprequalified candidate hash key 712. At block 1030, the signaturematcher 650 performs signature matching, as described above, to comparea portion of the current, previous and next reference signature blocks762-766 corresponding to the given prequalified candidate hash key 712with a site signature block containing the particular site signatureused to obtain the prequalified candidate hash key 712. At block 1035,the signature matcher 650 associates the site signatures in the sitesignature block with the reference media represented by the current,previous and next reference signature blocks 762-766 corresponding tothe given prequalified candidate hash key 712 if the matching performedat block 1030 was successful. At block 1040, the crediting facility 115causes processing to continue until all prequalified candidate hash keys712 have been processed. At block 1045, the signature matcher 150provides the successful signature matching results to further mediamonitoring process(es) (e.g., to credit the media monitored at themonitored site 120 as corresponding to the reference media representedby the reference signatures determined to match the site signatures atblock 1035).

An example program 1015P that may be executed to implement the examplecandidate qualifier 640 of the example crediting facility 115 of FIG. 6,and/or that may be used to perform the processing at block 1015 of FIG.10, is represented by the flowchart shown in FIG. 11. With reference tothe preceding figures and associated written descriptions, the exampleprogram 1015P of FIG. 11 begins execution at block 1105 at which thecandidate qualifier 640 obtains a group of candidate hash keys 712(e.g., corresponding to respective reference signatures) that werereturned in response to a query of the hash table 710 using a particularsite signature, as described above. At block 1110, the candidatequalifier 640 is configured to perform prequalification for each of thecandidate hash keys 712. For example, and as described above, at block1115, the candidate qualifier 640 compares the previous hash key 732included in the value data 730 for a given candidate hash key 712 withthe site signature preceding, in time, of the particular site signatureused to query the hash table 710. At block 1115, the candidate qualifier640 also compares the next hash key 736 732 included in the value data730 for a given candidate hash key 712 with the site signaturefollowing, in time, the particular site signature used to query the hashtable 710.

At block 1120, the candidate qualifier 640 determines if bothcomparisons performed at block 1115 were successful (e.g., if theprevious hash key 732 matched the previous site signature and the nexthash key 734 matched the subsequent site signature). If both comparisonswere successful (block 1120), at block 1125 the candidate qualifier 640indicates that the given candidate hash key 712 is prequalified for usein further signature matching processing for the current site signature.However, if either comparisons was unsuccessful (block 1120), at block1125 the candidate qualifier 640 causes the given candidate hash key 712to be excluded from use in further signature matching processing for thecurrent site signature. At block 1135, the candidate qualifier 640continues performing prequalification processing until all candidatehash keys 712 have been processed. At block 1140, the candidatequalifier 640 returns information identifying the resulting prequalifiedcandidate hash keys 712 (e.g., which correspond to respective referencesignatures).

FIG. 12 is a block diagram of an example processor platform 1200 capableof executing the instructions of FIGS. 9-11 to implement the examplesystem 100, the example crediting facility 115, the example mediadistributor(s) 105, the example monitored site(s) 120, the example MMS130, the example media device 205, the example device meter 210, theexample people meter 215, the example media receiver(s) 305, the examplesignature generator(s) 310, the example time determiner(s) 315, theexample data reporter 320, the example MMS interface 605, the examplehash table populator 610, the example block table populator 615, theexample hash table storage 620, the example block table storage 625, theexample site interface 630, the example hash table query processor 635,the example candidate qualifier 640, the example block table queryprocessor 645 and/or the example signature matcher 650 of FIGS. 1-8. Theprocessor platform 1200 can be, for example, a server, a personalcomputer, a mobile device (e.g., a cell phone, a smart phone, a tabletsuch as an iPad™), a personal digital assistant (PDA), an Internetappliance, a DVD player, a CD player, a digital video recorder, aBlu-ray player, a gaming console, a personal video recorder, a set topbox a digital camera, or any other type of computing device.

The processor platform 1200 of the illustrated example includes aprocessor 1212. The processor 1212 of the illustrated example ishardware. For example, the processor 1212 can be implemented by one ormore integrated circuits, logic circuits, microprocessors or controllersfrom any desired family or manufacturer.

The processor 1212 of the illustrated example includes a local memory1213 (e.g., a cache). The processor 1212 of the illustrated example isin communication with a main memory including a volatile memory 1214 anda non-volatile memory 1216 via a link 1218. The link 1218 may beimplemented by a bus, one or more point-to-point connections, etc., or acombination thereof. The volatile memory 1214 may be implemented bySynchronous Dynamic Random Access Memory (SDRAM), Dynamic Random AccessMemory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/or anyother type of random access memory device. The non-volatile memory 1216may be implemented by flash memory and/or any other desired type ofmemory device. Access to the main memory 1214, 1216 is controlled by amemory controller.

The processor platform 1200 of the illustrated example also includes aninterface circuit 1220. The interface circuit 1220 may be implemented byany type of interface standard, such as an Ethernet interface, auniversal serial bus (USB), and/or a PCI express interface.

In the illustrated example, one or more input devices 1222 are connectedto the interface circuit 1220. The input device(s) 1222 permit(s) a userto enter data and commands into the processor 1212. The input device(s)can be implemented by, for example, an audio sensor, a microphone, acamera (still or video), a keyboard, a button, a mouse, a touchscreen, atrack-pad, a trackball, a trackbar (such as an isopoint), a voicerecognition system and/or any other human-machine interface. Also, manysystems, such as the processor platform 1200, can allow the user tocontrol the computer system and provide data to the computer usingphysical gestures, such as, but not limited to, hand or body movements,facial expressions, and face recognition.

One or more output devices 1224 are also connected to the interfacecircuit 1220 of the illustrated example. The output devices 1224 can beimplemented, for example, by display devices (e.g., a light emittingdiode (LED), an organic light emitting diode (OLED), a liquid crystaldisplay, a cathode ray tube display (CRT), a touchscreen, a tactileoutput device, a light emitting diode (LED), a printer and/or speakers).The interface circuit 1220 of the illustrated example, thus, typicallyincludes a graphics driver card, a graphics driver chip or a graphicsdriver processor.

The interface circuit 1220 of the illustrated example also includes acommunication device such as a transmitter, a receiver, a transceiver, amodem and/or network interface card to facilitate exchange of data withexternal machines (e.g., computing devices of any kind) via a network1226 (e.g., an Ethernet connection, a digital subscriber line (DSL), atelephone line, coaxial cable, a cellular telephone system, etc.).

The processor platform 1200 of the illustrated example also includes oneor more mass storage devices 1228 for storing software and/or data.Examples of such mass storage devices 1228 include floppy disk drives,hard drive disks, compact disk drives, Blu-ray disk drives, RAID(redundant array of independent disks) systems, and digital versatiledisk (DVD) drives.

Coded instructions 1232 corresponding to the instructions of FIGS. 9-11may be stored in the mass storage device 1228, in the volatile memory1214, in the non-volatile memory 1216, in the local memory 1213 and/oron a removable tangible computer readable storage medium, such as a CDor DVD 1236.

Example methods, apparatus, systems and articles of manufacture toperform signature retrieval and matching for media monitoring have beendisclosed herein. Further example techniques to identify media usinghash keys, which can be employed in conjunction with the examplesprovided herein, are disclosed in U.S. Provisional Application Ser. No.61/976,238 (Attorney Docket No. 20004/103754US01), entitled “METHODS ANDAPPARATUS TO IDENTIFY MEDIA USING HASH KEYS” and filed on Apr. 7, 2014,which is hereby incorporated by reference in its entirety.

Although certain example methods, apparatus and articles of manufacturehave been disclosed herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus and articles of manufacture fairly falling within the scope ofthe claims of this patent.

What is claimed is:
 1. An apparatus comprising: means for querying afirst table to perform a first query of the first table using a hashcorresponding to a first site signature, the first site signatureobtained from a monitored site, the first table including hash keyscorresponding to respective reference signatures, the first query toobtain, from the first table, first qualifier data descriptive of afirst reference signature corresponding to a first hash key that matchesthe hash corresponding to the first site signature; means for querying asecond table to perform a second query of the second table using thefirst qualifier data obtained from the first query of the first table,the second query to obtain, from the second table, a plurality of blocksof reference signatures, the second table different than the firsttable; means for comparing a first block of site signatures with aportion of the plurality of blocks of reference signatures, the firstblock of site signatures to include the first site signature; and meansfor crediting media, monitored at the monitored site, as correspondingto reference media represented by the first reference signature when thefirst block of site signatures matches the portion of the plurality ofblocks of reference signatures.
 2. The apparatus as defined in claim 1,wherein the first qualifier data includes a first timestamp associatedwith a first block of reference signatures including the first referencesignature, the first qualifier data also including first mediaidentification data identifying first reference media represented by thefirst reference signature.
 3. The apparatus as defined in claim 2,wherein the plurality of blocks of reference signatures obtained fromthe second query of the second table using the first qualifier datainclude: the first block of reference signatures representative of thefirst reference media and associated with the first timestamp; a secondblock of reference signatures representative of the first referencemedia and associated with a second timestamp preceding the firsttimestamp; and a third block of reference signatures representative ofthe first reference media and associated with a third timestampfollowing the first timestamp.
 4. The apparatus as defined in claim 3,wherein the first qualifier data further includes a first offsetspecifying a position of the first reference signature in the firstblock of reference signatures, the first block of site signaturesincludes neighboring site signatures of the first site signature, andthe means for comparing is further to: align the first block of sitesignatures with a portion of the first, second and third blocks ofreference signatures based on the first offset; and compare the firstblock of site signatures with the portion of the first, second and thirdblocks of reference signatures.
 5. The apparatus as defined in claim 1,wherein the first reference signature is representative of firstreference media, the plurality of blocks of reference signatures is afirst plurality of blocks of reference signatures representative of thefirst reference media, and: the means for querying the second table isto query the second table using second qualifier data obtained from thefirst query of the first table, the second qualifier data descriptive ofa second reference signature corresponding to a second hash keydetermined to match the hash corresponding to the first site signature,the second reference signature being representative of second referencemedia; and the means for comparing is to compare the first block of sitesignatures with a second plurality of blocks of reference signaturesobtained from the query of the second table using the second qualifierdata, the second plurality of blocks of reference signaturesrepresentative of the second reference media.
 6. The apparatus asdefined in claim 1, wherein the means for querying the first table is toobtain the first hash key, the first qualifier data and first value dataassociated with the first hash key in response to the first query of thefirst table, and further including means for qualifying the first valuedata to prequalify the first hash key as a candidate for subsequentsignature processing associated with the first site signature.
 7. Theapparatus as defined in claim 6, wherein: the means for querying thefirst table is to obtain a second hash key, second qualifier data andsecond value data associated with the second hash key in response to thefirst query of the first table, the second hash key having beendetermined to match the first site signature, the second qualifier datadescriptive of a second reference signature corresponding to the secondhash key; and the means for querying the second table is to: query thesecond table using the second qualifier data in response to a successfulprequalification of the second hash key based on the second value data;and not query the second table using the second qualifier data inresponse to an unsuccessful prequalification of the second hash keybased on the second value data.
 8. The apparatus as defined in claim 6,wherein the first reference signature is representative of firstreference media, the first value data includes a second hash key and athird hash key both representative of the first reference media, thesecond hash key preceding the first hash key in time and the third hashkey following the first hash key in time, and the means for qualifyingis to: determine prequalification of the first hash key is successful inresponse to the second hash key having matched a second site signaturepreceding the first site signature in time and the third hash key havingmatched a third site signature following the first site signature intime; and determine prequalification of the first hash key isunsuccessful in response to at least one of the second hash key havingnot matched the second site signature or the third hash key having notmatched the third site signature.
 9. An apparatus comprising: means forpopulating a hash table to: store hash keys representative of respectivereference signatures included in a first reference signature blockassociated with first reference media in respective entries of a hashtable in a database; and store first qualifier data in a first entry ofthe hash table corresponding to a first hash key, the first qualifierdata to include a timestamp, a first offset, and an identifierassociated with a first reference signature represented by the firsthash key; and means for populating a block table to: store a first blocktable key corresponding to the first reference signature block in afirst entry of a block table in the database, the first block table keyto include the timestamp and the identifier; and store the firstreference signature block, a preceding reference signature blockrelative to the first reference signature block and a subsequentreference signature block relative to the first reference signatureblock in the first entry of the block table; and means for accessing thehash table and the block table to retrieve candidate referencesignatures to compare with site signatures representative of monitoredmedia to identify the monitored media.
 10. The apparatus as defined inclaim 9, wherein the means for populating the hash table is to store, inthe first entry of the hash table, a second hash key representative of asecond reference signature preceding the first reference signature inthe first reference signature block and a third hash key representativeof a third reference signature following the first reference signaturein the first reference signature block.
 11. The apparatus as defined inclaim 9, wherein the first offset corresponds to a position of the firstreference signature in the first reference signature block.
 12. Theapparatus as defined in claim 9, wherein the hash table is stored in afirst type of memory and the block table is stored in a second,different type of memory.
 13. The apparatus as defined in claim 12,wherein the first type of memory is volatile memory and the second typeof memory is non-volatile memory.
 14. The apparatus as defined in claim9, further including means for processing to: perform hash tablecompaction to purge out-of-date reference data from the hash table; andperform block table compaction to purge out-of-date reference data fromthe block table.
 15. The apparatus as defined in claim 14, wherein themeans for processing is to perform at least one of the hash tablecompaction or the block table compaction based on a time-to-live value.16. An apparatus comprising: memory to include machine executableinstructions; and processor circuitry to execute the machine executableinstructions to at least: perform a first query at a first table using ahash corresponding to a first site signature, the first site signatureobtained from a monitored site, the first table including hash keyscorresponding to respective reference signatures, the first query toobtain, from the first table, first qualifier data descriptive of areference signature corresponding to a first hash key that matches thehash corresponding to the first site signature; perform a second queryat a second table using the first qualifier data obtained from the firstquery of the first table, the second query to obtain, from the secondtable, a plurality of blocks of reference signatures, the second tabledifferent than the first table; compare a first block of site signatureswith a portion of a plurality of blocks of reference signatures, thefirst block of site signatures to include the first site signature; andcredit media, monitored at the monitored site, as corresponding toreference media represented by the first reference signature when thefirst block of site signatures matches the portion of the plurality ofblocks of reference signatures.
 17. The apparatus as defined in claim16, wherein the first qualifier data includes a first timestampassociated with a first block of reference signatures including thefirst reference signature, the first qualifier data also including firstmedia identification data identifying first reference media representedby the first reference signature.
 18. The apparatus as defined in claim17, wherein the plurality of blocks of reference signatures obtainedfrom the second query of the second table using the first qualifier datainclude: the first block of reference signatures representative of thefirst reference media and associated with the first timestamp; a secondblock of reference signatures representative of the first referencemedia and associated with a second timestamp preceding the firsttimestamp; and a third block of reference signatures representative ofthe first reference media and associated with a third timestampfollowing the first timestamp.
 19. The apparatus as defined in claim 18,wherein the first qualifier data further includes a first offsetspecifying a position of the first reference signature in the firstblock of reference signatures, the first block of site signaturesincludes neighboring site signatures of the first site signature, andthe processor circuitry is to: align the first block of site signatureswith a portion of the first, second and third blocks of referencesignatures based on the first offset; and compare the first block ofsite signatures with the portion of the first, second and third blocksof reference signatures.
 20. The apparatus as defined in claim 16,wherein the first reference signature is representative of firstreference media, the plurality of blocks of reference signatures is afirst plurality of blocks of reference signatures representative of thefirst reference media, and the processor circuitry is to: query thesecond table using second qualifier data obtained from the first queryof the first table, the second qualifier data descriptive of a secondreference signature corresponding to a second hash key determined tomatch the hash corresponding to the first site signature, the secondreference signature being representative of second reference media; andcompare the first block of site signatures with a second plurality ofblocks of reference signatures obtained from the querying of the secondtable using the second qualifier data, the second plurality of blocks ofreference signatures representative of the second reference media.